1. Field of the Invention
The present invention relates to a steam turbine forced air cooling system for forcibly cooling a steam turbine after the shutdown of the steam turbine, a steam turbine provided with the system, and a method of the steam turbine forced air cooling.
2. Description of the Related Art
A steam turbine introduces high-temperature steam of 500 degrees Celsius or higher at a steam turbine inlet portion. Such a steam turbine requires disassembly operation at the time of routine inspection or failure of the turbine itself. It would take a considerable period of time if the steam turbine is cooled through natural heat-release to a temperature at which turning can be stopped. In addition, electric power cannot be supplied in such a period of time. It is hence desirable to shorten a cooling-down period as much as possible with the stable supply and economic efficiency of electric power taken into consideration.
JP-1991-4723-B describes the following technology as a method of cooling steam turbine. The vacuum pump connected to the condenser is driven to apply suction power to the exhaust passage. The outside air is then sucked into the condenser from the vacuum breaker. This outside air passes through the LP turbine from the condenser and enters the inside of the IP turbine from the steam exhaust portion of the IP turbine. The outside air cools the IP turbine from the low temperature side thereof to increase in temperature. The outside air with increased temperature flows toward the high temperature side of the IP turbine to cool the high temperature side thereof and is discharged into the exhaust passage from the steam introduction portion of the IP turbine. Meanwhile, the outside air sucked into the condenser passes through the ventilator valve and the cold reheat pipe, enters the HP turbine from the steam exhaust portion thereof to cool the HP turbine, and is discharged into the exhaust passage from the steam introduction portion. JP-1991-4723-B describes the technology in which the ejector in place of the vacuum pump is connected to the condenser.